Magnetic sound record



Dec. 23, 1952 T. H. MANN ETAL Re. 23,602

MAGNETIC SOUND RECORD Original Filed April 20, 1948 INVENTORS ATTORNEYReissuecl Dec. 23, 1952 MAGNETIC SOUND RECORD Theodore H. Mann andTheodore G. Mann, Los Angeles, Calif., assignors to Sound Engineering,Hollywood, Calif., a partnership Original No 2,581,765, dated January 8,1952, Se-

rial No. 22,078, April 20, 1948. Application for reissue July 5, 1952,Serial No. 297,414

6 Claims.

Matter enclosed in heavy brackets I: 1 appears in the original patentbut forms no part of this reissue specification; matter printed initalics indicates the additions made by reissue.

This invention relates to magnetic sound recording and in particular toa form for the face of the record base upon which a magnetic recordingmay be recorded and reproduced without the use of any driving mechanismfor moving the head across the face.

Magnetic recording has many advantages over other recording methods butits general use has been restricted heretofore by the fact that magneticrecording materials in the usual form such as wire or tape or plainsurfaced discs or cylinders require specialized driving mechanism toadvance the recording or playing head on the spiral or helix.Heretofore, it has not been possible to use in connection with magneticrecordings, the existing recording and play-back equipment which iscommonly available in phonograph record players because in these thepointed stylus follows a pre-formed spiral or helical groove and doesnot require a cross feeding mechanism such as that required in magneticrecordings on, for example, plain discs.

The principal object of this invention is to provide a surface on a diskor cylinder adapted for magnetic recording which can be recorded orplayed by utilizing available phonograph equipment upon which there hasbeen substituted a magnetic type recording or play-back head.

In accordance with this invention, a magnetic recording base is made upin disk or cylinder form similar in size to ordinary phonograph recordsof these types and is provided with a spiral groove of special sawtoothed cross-sectional shape, which is engaged by the contacting footof the translating magnetic head, which is shaped on one side to ride inthe bottom of the groove and against the steeper wall of the groove,while the other side of the foot passes closely adjacent the longer andflatter wall of the groove surface, on which flatter wall the magneticrecord is impressed.

The recording base may be made in a number of ways depending on thecharacteristics of the particular structural material used, the standardof quality desired in the recording and reproduction and in the type ofservice for which the recording is to be used.

The invention will be described in relation to a grooved disk typerecording base, although any form of continuous curved groove type basessuch as disks or cylinders may also be used, reference being made to theaccompanying drawings in which:

Fig. 1 is an enlarged cross-sectional view showing the saw toothedgrooves made in a uniform base material;

Fig. 2 is an enlarged cross-sectional view showing the saw toothedshaped grooves, the flatter surfaces only having a relatively thin layerof magnetic recording material thereon;

Fig. 3 is a side elevational view of a typical recording or translatingmagnetic head; and

Fig. 4 is a cross-sectional view showing the contacting foot of therecording head in contact with one saw-toothed groove of the recordbase.

Figure 1 shows a record base of suitable magnetic material throughout inwhich the spiral saw-toothed grooves are formed either in the pressingof the blanks or by cutting the grooves previous to making the magneticrecording. In Figure 2 is shown a form of my invention in which therecord body may be made of any suitable material such as syntheticplastic, glass, ceramic or non-magnetic metals, the flatter wall surfaceof the saw-toothed groove being coated with a layer l2 of suitablemagnetic recording material deposited on or otherwise affixed to theflatter groove face. In this form, the spiral groove with saw-toothedcross-section is preformed on the flat face of the body of the materialby any suitable process such as by pressing or by cutting.

One method of forming a record body of the type shown in Figure 2 is topre-form saw-toothed shaped grooves in a non-magnetizable base; thenfill the grooves with a magnetizable coating material, followed byrecutting the grooves to leave the magnetizable material only on theflatter wall of the groove. Another method of preparing the record baseconsists in forming a homogeneous dispersion of magnetic material in ares inous binding and dispersing material such as styrene, vinylite andthe like, and then pressing the body in forming dies which impress thesawtoothed grooves in the surface or surfaces. One composition which hasbeen found to be satisfactory for this purpose consists of about '70parts by weight of ferric oxide powder, 30 parts by weight of styrene,and .5 part by weight of lead stearate.

By using a saw-toothed shaped groove on whose flatter wall the magneticrecording is made, the magnetic head is guided along the pre-formedspiral by the foot I5 which rides in the bottom I6 of the groove andalso in the steeper wall H, which may or may not be covered withmagnetic recording material. The foot of the recorder or translatingmagnet is guided by the steeper wall I! of the spiral groove so that thetranslating magnet is carried over the entire length of the spiralgroove without mechanical transverse spiral guiding mechanisms.

In other words, the

ordinary stylus supporting arm of a phonograph which is arranged bysuitable pivoted joints to follow a spiral groove by moving in an arcacross the disk as the stylus follows the spiral groove may be utilizedfor supporting the magnetic head, with the specially shaped foot lfollowing the bottom of the groove, and with a side thrust against thesteeper wall 11.

Any suitable type of magnetic recording or translating device having asuitably shaped foot to pass along the saw-toothed shaped grooves may beused. An illustrative translating magnet is shown in Figure 3, with adetailed cross-sectional view of the foot shown in Figure 4.

The magnetizable composition for the recording base, either for thesingle layer record of Figure 1, or for the double layer form of Figure2, may consist of any suitable non-magnetic material such as celluloseacetate, vinyl-type plastics, etc., in which there is distributed ironor iron-oxide particles of a kind and in suitable concentration to beeifective as a magnetic recording material, following the well knownpractices of this art.

The advantages of our invention will be apparent. The use of apre-formed saw-toothed groove, one wall of which serves as the magneticrecording surface and the other wall of which acts to guide the magnetichead in a spiral or helical path, gives a maximum length of recordingsurface on a given sized disk or cylinder, since no space is requiredfor lands between the grooves.

When a record base of the type shown in Figure 2 is used, the undesiredecho effect is avoided. Groove echo is the result of spreadingthemagnetization beyond the desired boundaries, and this is minimized inthe saw-toothed groove design because the edges of the magnetizablecoating are spaced a maximum distance away from those of the adjoininggroove edges. The use of the saw-toothed grooved records facilitates theconversion of the ordinary phonograph player to us magnetic recordingsand playings, because no cross-feeding mechanism is required, and thesupporting arm of the usual mechanical stylus may be used as asupporting arm for the magnetic head.

Where the expression continuous curved groove is used in thisapplication, both regular and irregular spiral grooves and helicalgrooves are included.

We claim:

1. A magnetic sound record comprising a continuous solid record basehaving thereon a continuous [curved] groove of non-equilateral sawtoothcross-sectional shape, at least one wall surface of said groove beingadapted to receive magnetic sound recordings and [the adjacentconvolutions of said continuous curved groove] being contiguous at acommon edge with adjacent groove structure of cross-sectional shape andorientation similar to said continuous groove.

2. A magnetic sound record comprising a continuous solid record basehaving thereon a continuous curved groove of non-equilateral sawtoothcross-sectional shape, at least one wall surface of said groove having acoating of magnetic recording material and the adjacent convolutions ofsaid continuous curved groove being contiguous at a common edge.

3. A magnetic sound record comprising a continuous solid record basehaving thereon a continuous curved groove of non-equilateral sawtoothcross-sectional shape, at least the wall surface of said groove havingthe lesser inclination from the horizontal being adapted to receivemagnetic sound recordings and the adjacent convolutions of saidcontinuous curved groove being contiguous at a common edge.

. 4. A magnetic sound record comprising a continuous solid record basehaving thereon a continuous curved groove of non-equilateral sawtoothcross-sectional shape, at least the wall surface of said groove havingthe lesser inclination from the horizontal being provided with a coatingof magnetic recording material and the adjacent convolutions of saidcontinuous curved groove being contiguous at a common edge.

5. A magnetic sound record comprising a homogeneous continuous solidrecord base of magnetic recording material, said base having thereon acontinuous curved groove of non-equilateral saw-tooth cross-sectionalshape, one wall surface of said groove being adapted to receive magneticsound recordings and the adjacent convolutions of said continuous curvedgroove being contiguous at a common edge.

6. A magnetic sound record comprising a homogeneous continuous solidrecord base of magnetic recording material, said base having thereon acontinuous curved groove of non-equilateral saw-tooth cross-sectionalshape, the wall surface of said groove having the lesser inclinationfrom the horizontal being adapted to receive magnetic sound recordingsand the adjacent convolutions of said continuous curved groove beingcontiguous at a common edge.

THEODORE H. MANN. THEODORE G. MANN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 907,383 Lieb Dec. 22, 19081,074,424 Fessendon Sept. 30, 1913 1,609,540 Goddard et a1 Dec. '7, 19261,912,887 Chipman June 6, 1933 2,247,847 Pfieumer July 1, 1941 2,381,463Potter Aug. '7, 19 5

